Pulse oximeter displays blood oxygen levels on a PC

The last time you were in the emergency room after a horrible accident involving a PVC pressure vessel, a nurse probably clipped a device called a pulse oximeter onto one of your remaining fingers. These small electronic devices detect both your pulse and blood oxygen level with a pair of LEDs and a photosensor. [Anders] sent in a great tutorial for building your own pulse oximeter using a fancy ARM dev board, but the theory behind the operation of this device can be transferred to just about any microcontroller platform.

The theory behind a pulse oximeter relies on the fact that hemoglobin absorbs red and infrared light differently based on its oxygenation levels. By shining a red and IR LED through a finger onto a photoresistor, it’s possible to determine a person’s blood oxygen level with just a tiny bit of math.

Of course a little bit of hardware needs to be thrown into the project; for this, [Anders] used an EMF32 Gecko starter kit, a great looking ARM dev board. After connecting the LEDs to a few transistors and opamps, [Anders] connected his sensor circuit to the ADC on the Gecko board. From here it was very easy to calculate his blood oxygen level and even display his pulse rate to a PC application.

Yes, for just the price of a dev board and a few LEDs, it’s possible to build your own medical device at a price far below what a commercial pulseox meter would cost. FDA approval not included.

OLYMPIA — The Department of Labor and Industries warned today that plastic polyvinyl chloride (PVC) pipe cannot be used in compressed air piping systems without the risk of explosion.

When PVC piping explodes, plastic shrapnel pieces are thrown in all directions.

“We’re seeing more incidents of explosive failure, and we’re citing more employers for using PVC air system piping,” said Paul Merrill, senior safety inspector in L&I’s Spokane office.

“It’s probably just a matter of time before someone gets seriously injured in one of these explosions unless everyone pays more attention to the manufacturer’s warnings,” Merrill said.
Last year, a section of PVC pipe being used for compressed air exploded 27 feet above a warehouse floor. A fragment of the pipe flew 60 feet and embedded itself in a roll of paper. Fortunately, nobody was in the area at the time.
A PVC pipe explosion in a new plant in Selah broke an employee’s nose and cut his face.

Only one type of plastic pipe has been approved for use with compressed air. That pipe, Acrylonitrile-Butadiene-Styrene (ABS), is marked on the pipe as approved for compressed air supply.

By law, employers must protect their workers by avoiding the use of unapproved PVC pipe in such systems. Existing compressed air systems which use PVC piping must be completely enclosed, buried or adequately guarded according to specifications approved by a professional consulting engineer.

NOTICE TO EMPLOYERS: If you have questions about the suitability of a material for air system piping, call Labor and Industries at the number listed above for a free consultation.

NOTICE TO EMPLOYEES: If you suspect that a pressurized PVC piping hazard exists, bring it to the attention of your employer. If you do not obtain satisfactory results, you may file a confidential complaint with the Department of Labor and Industries. Complaints are investigated promptly.

The Dallas Regional Office has brought to our attention a potential serious hazard existing with the use of polyvinyl chloride (PVC) plastic pipes for transporting compressed gases in above ground installations. An employee in a Texas plant was injured recently by a rupture in a PVC compressed air line. Plastic projectiles from the point of rupture caused lacerations of the employee’s hand. This is noteworthy because the Plastic Pipe Institute, in its Recommendation B dated January 19, 1972, recommends against the use of thermoplastic pipe to transport compressed air or other compressed gases in exposed plant piping. (See attachment.)

Furthermore, sections 842.32, 842.43 and 849.52(b) of the American National Standards Institute/American Society of Mechanical Engineers (ANSI/ASME) B31.8-1986, Gas Transmission and Distribution Piping Systems Standard, limit the operating pressure of plastic piping distribution systems to 100 pounds per inch (psi) and prohibit the installation of such systems above ground except where “. . . the above ground portion of the plastic service line is completely enclosed in a conduit or casing of sufficient strength to provide protection from external damage and deterioration.” (Excerpts attached.)

In response to your recent inquiry concerning our regulatory position on the use of plastic pipe for compressed air systems, I trust this letter will clear up any confusion over the issue.

It is our position that PVC pipe shall not be used as a means of transporting compressed air. This position follows the manufacturer’s own statements that PVC is unsuitable for compressed air systems. We do allow the use of certain ABS materials that are specifically designed for compressed air systems. One such product is “Duraplus” air line piping system ABS pipe. However, as in any such system, the manufacturer’s specifications on acceptable pressure and temperature considerations must be followed.

In closing, misapplication of a product, such as using PVC for compressed air systems, may result in citations and penalties being issued dependent upon the specific conditions.

I appreciate your concern and inquiry into this potential safety hazard.

It has recently come to my attention that there is a severe safety regarding the improper usage of plastic polyvinyl chloride (PVC) pipe. This pipe is designed for the transmittal of liquids, and is dangerous when used for transmitting compressed air or gas. Unfortunately, PVC has been frequently used with compressed air in construction projects across the country.

The state of Washington has notified the public that PVC pipe is not to be used in compressed air systems. I have also learned that the state of Nevada is in the process of making a similar determination and announcement. Additionally manufacturers of this product advise against its use with compressed air in their catalogue publications.

I believe that it is in the best interests of the citizens of our state if your office would expeditiously make such an announcement. A notice to users of the hazards of PVC pipe – when used improperly – would have the effect of preventing possible severe injury to people who work with or near this product.

By way of this letter, I am contacting the Department of Labor, OSHA, in Washington, D.C. and asking their officials to report to me on actions taken on the Federal level to restrict the use of this pipe and to notify users of the potential hazards involved in improper use of PVC pipe.

Your timely consideration of this request is appreciated.

Sincerely,

DENNIS DeCONCINI
United States Senator

STATE OF WASHINGTON
Department of
Labor & Industries
Hazard Alert

For more information, call: 1-800-423-7233

FOR IMMEDIATE RELEASE May 26, 1988

PVC pipe not to be used in compressed air systems

OLYMPIA — The Department of Labor and Industries warned today that plastic polyvinyl chloride (PVC) pipe cannot be used in compressed air piping systems without the risk of explosion.

When PVC piping explodes, plastic shrapnel pieces are thrown in all directions.

“We’re seeing more incidents of explosive failure, and we’re citing more employers for using PVC air system piping,” said Paul Merrill, senior safety inspector in L&I’s Spokane office.

“It’s probably just a matter of time before someone gets seriously injured in one of these explosions unless everyone pays more attention to the manufacturer’s warnings,” Merrill said.

Last year, a section of PVC pipe being used for compressed air exploded 27 feet above a warehouse floor. A fragment of the pipe flew 60 feet and embedded itself in a roll of paper. Fortunately, nobody was in the area at the time.

A PVC pipe explosion in a new plant in Selah broke an employee’s nose and cut his face.

Only one type of plastic pipe has been approved for use with compressed air. That pipe, Acrylonitrile-Butadiene-Styrene (ABS), is marked on the pipe as approved for compressed air supply.

By law, employers must protect their workers by avoiding the use of unapproved PVC pipe in such systems. Existing compressed air systems which use PVC piping must be completely enclosed, buried or adequately guarded according to specifications approved by a professional consulting engineer.

NOTICE TO EMPLOYERS: If you have questions about the suitability of a material for air system piping, call Labor and Industries at the number listed above for a free consultation.

NOTICE TO EMPLOYEES: If you suspect that a pressurized PVC piping hazard exists, bring it to the attention of your employer. If you do not obtain satisfactory results, you may file a confidential complaint with the Department of Labor and Industries. Complaints are investigated promptly.

We have recently been made aware of a potentially serious hazard involving the prohibited use of unprotected plastic (PVC( piping to transport compressed air and other compressed gases in above ground installations.

While in Arizona we are not aware of any incidents of ruptured or exploding plastic pipes, States such as Washington and Texas have experienced incidents and injuries. Despite the lack of incidents in Arizona, we full recognize the potential for similar occurrences in this State and thereby request that you review your facilities and replace any such unsafe installations.

The Arizona Division of Occupational Safety and Health will be providing a program of awareness, assistance, and enforcement. This notice will be going to representatives of industry associations, labor organizations, print and electronic media.

Through our consultation and training program we will be providing assistance based upon requests received from employers. Through our compliance programs, we will be conducting unannounced inspections to ensure compliance with manufacturers’ specifications and American National Standards Institute and American Society of Mechanical Engineers’ Standard B 31.8-1986, which limits the operating pressure of plastic piping distribution systems to 100 pounds per square inch (psi) and prohibits the installation of such systems above ground except where the above ground portion of the plastic service line is enclosed in a conduit or casing of sufficient strength to provide protection from external damage and deterioration.

If you need assistance, please don’t hesitate to call the Industrial Commission’s Arizona Division of Occupational Safety and Health at 255-5795.

RECOMMENDATION B
THERMOPLASTIC PIPING
FOR THE TRANSPORT OF COMPRESSED AIR
OR OTHER COMPRESSED GASES

Adopted January 19, 1972

The Plastics Pipe Institute recommends against the use of thermoplastic pipe to transport compressed air or other compressed gases or the testing of such piping with compressed air or other compressed gases in exposed above ground locations, e.g. in exposed plant piping. It is recommended that all thermoplastic piping used to transport compressed air or other compressed gases be buried underground or encased in shatter-resistant materials. In designing thermoplastic piping to transport compressed air or other compressed gases, the strength at the operating temperature, the pressure, the energetics, and specific failure mechanism need to be evaluated.

Colonial Engineering Inc.
Thermoplastic Piping Systems

To Whom It May Concern:

From time to time, I receive inquiries as to the suitability of using PVC pipe land fittings in compressed gas piping systems. While the benefits of use may be enticing, it is a very dangerous and, in some states, illegal thing to do. For example, MIOSHA (Michigan’s branch of OSHA) prohibits the use of PVC plastic in compressed gas systems unless properly encased in steel, cement, or some other approved material. Please check your local and state regulations.

The main problem with using PVC pipe and fittings for compressed gas is not that it spontaneously explodes but that PVC is a brittle material that can be broken or shattered with external force unless properly protected. Compressed gasses can be best described as being analogous to a coiled spring. When a PVC pipe or fitting fails when under stress from compressed gas it literally explodes like a bomb, sending shards of plastic flying several feet in all directions. Liquids, on the other hand, being compressed by only 1/10th of 1% contain very little stored energy. When pressurized systems with liquids fail, the energy is dissipated very quickly, thereby creating a much lower potential for hazard.

Colonial Engineering does not recommend the use of PVC plastic pipe fittings in compressed gas service.

If you have further questions regarding this matter please feel free to contact me directly.

The dangers involved in using rigid vinyl piping products for compressed air transport are well known in our industry. Numerous disclaimer bulletins and letters have been circulated for almost three decades. It will not surprise you to learn that our government has just recently recognized the problem.

Attached you will find a copy of a memorandum that was issued by the “U.S. Dept. of Labor, Occupation Safety & Health Administration” (OSHA). You may wish to give copies to your customers and any other interested party. The government has finally made this danger “official.”

I am alerting you that there is a device on the market for pressure testing product lines, used in conjunction with tank testing, which is not safe. This device, manufactured by Horner Creative Products, 413 State Park Drive, Bay City, Michigan 48706, utilizes a plastic (PVC) cylinder which is attached to the pipeline, filled with gasoline, and then up to 100 PSI air pressure applied to the cylinder.

Not only have the manufacturers of PVC indicated for years that “extreme dangers” are involved because of its potential to explode, but they have notified Mr. Horner via their distributors, that they do not want him using their material (PVC) to make his line tester. He has thumbed his nose at the manufacturers of PVC, and continues to market this product. The use of PVC for compressed air or gas systems has been prohibited by several states – copies of their hazard alerts enclosed.

As a responsible regulator it is only proper that you be aware of this device being utilized nationwide by hundreds of unsuspecting operators. I have documented three failures of this product line tester to date. Fortunately no injuries have yet occurred, but there is obviously an imminent danger to the operator and to the public. There have been documented cases of similar misuse of PVC in compressed air or gas systems where injuries have occurred.

Please, before someone gets killed, or seriously hurt, help remove this product from the marketplace. Obviously Mr. Horner will not remove it without pressure being applied from you.

Should you have further questions, or I can be of further service, please feel free to call on me.

That was a 2″ cannon I made a few years ago. It exploded while I was holding it between my legs. The barrel kicked back and upwards into my crotch, and PVC shards flew everywhere. I have a scar on my right foot as a result of one of the shards penetrating my shoe and slicing the top and side of my foot.

This is in response to your memorandum of January 17, concerning a recently issued [Safety and Health Information Bulletin (SHIB)] dated December 13, 1990, by the [Directorate of Science, Technology and Medicine]. The SHIB was issued in connection with the use of thermoplastic pipes in above ground transportation of compressed air or gases, and was based on the Plastic Pipe Institute’s recommendation, dated December 1, 1989.

You indicated in your memorandum that various companies in your Region are misinterpreting the SHIB to imply that regular polyvinyl chloride (PVC) pipes that are designed to meet American Society for Testing and Materials (ASTM) Standard D1785-86, can be used for transportation of compressed air and gases. The SHIB, however, means that the pipes must either be constructed of or be encased in shatter resistant materials.

You requested an official citation issuance policy regarding the use of PVC pipes for above ground transportation of compressed air or gases. You also requested our office to describe a citation scenario.

Since PVC material does not possess shatter resistant property, and since it is very clear from the industry’s recognized practice that PVC pipes are prohibited for above ground transportation of compressed air and gases (unless the pipelines are encased in shatter resistant material), any such use by the employers, where employees may be exposed to hazards, will be in violation of Section 5(a)(1) of the OSH Act. Therefore, employers who are found to violate the above described conditions or manufacturer’s recommendations, during an OSHA inspection, shall be issued a 5(a)(1) citation.

For any further clarifications, please have your staff members contact [the Office of General Industry Enforcement at 202-693-1850].

That’s about US$66. The basic clamp-on-your-finger pulse oximeter I bought from Amazon cost US$25-30; if you want something with a computer interface, the cheapest I’ve seen is about $100, but there may be better choices now.

It’s not perfect, but this is waaaaay better than the crap diy “pulse oximeters” I normally see (most of which show no knowledge on the circuit design or physics) and are usually just photoplethysmographs. This, however, is a proper pulse oximeter.

For those who are curious: the reason 2 LEDs are used, and at those particular wavelengths, is because they represent wavelengths at which the difference in absorptivity between the hemoglobin and oxyhemoglobin are greatest for both signs of the difference. This means that (a) any offset due to ambient light is automatically removed, (b) the output value isn’t affected by overall changes in absorption due to pressing the LEDs closer, or moving the sensor between an ear or a finger.

Just a question, if the PVC pressure vessel explosion blew off all your fingers could you put the pulse oximeter on on your nose, or your toes or anything else conveniently dangley? I’m assuming if the light sensor can get a light reading it should work?

Any tissue that allows light transmission and contains sufficient capillaries. With a strong enough light, you could go right through the palm of your hand (i think they do this with babies, at least maybe with premature ones….but that could be in my imagination). But, like the other comment said, earlobe is the common alternative.

Interestingly, you can also make these measures by looking at the reflected light from your skin. However, for a bunch of reasons, this is more complicated…